Every once in a while after scanning a slide I see numerous small black spots. I have tried brushing, canned air and two different negative cleaners to no effect. Again -- it isn't all my slides that have these black spots. Could it be a processing problem? I mainly shot Kodachrome 64 and they were all processed in Texas.

I use a soft lens brush on my slides before scanning, and usually a few black spots persist. Most times, I believe that they are dust particles that are more firmly stuck to the film, but I have also heard of cases where Kodachromes have developed a "mold" in the emulsion. I have seen a very few of my slides that may be exhibiting this issue, and that's the reason that I have begun a very long-term project to digitize my entire collection.

No matter what the cause, I clone out the remaining spots while processing in Lightroom.

You also may be seeing small spots that seem to develop in the skies of some of my photos. I think these are possibly film imperfections, and they will fade away if you lighten the sky. They also disappear if you blur the sky using the adjustment brush.